Can anyone explain to me how it possible that when i have a file that i cannot read on my computer because of a missing codec, then i installed the proper codec and after that i can read it with only SOME software. Other still are not able to read the same file ? (and i'm talking about software that should read this kind of file ie: mpg or avi like windows media player, classic media player, virtual dub, ulead video studio etc. )

Don't they all suppose to use the same codec (in a windows sub directory) ?